Mordant Blade

Weapon (any weapon that deals slashing damage), rare (requires attunement)

You can use a bonus action to speak this magic weapon’s command word, causing the blade to weep a caustic, green acid. While weeping acid, the weapon deals an extra 2d6 acid damage to any target it hits. The weapon continues to weep acid until you use a bonus action to speak the command word again or you sheathe or drop the weapon.

Acid Arc. While holding the weapon, you can use an action to swing it in a wide arc, spraying acid in a 15-foot cone. Each creature in the cone must make a DC 15 Dexterity saving throw, taking 4d6 acid damage on a failed save, or half as much damage on a successful one. Once used, this property can’t be used again until the next dawn.